Generally, from the view point of intended pharmacological activities, side-effects and the like, pharmaceutical compounds having an asymmetric center in the molecule are desirable to be used in their optically active form instead of in racemic form. A racemic naphthalene compound (Patent literature 1) represented by general formula [A]:
which is known to possess cAMP-specific phosphodiesterase (PDE4) inhibitory activity and be useful as anti-asthma drugs and the like, has one asymmetric carbon atom in the molecule, and therefore it is considered that the compound is desirable to be applied to clinical use in the optically active form.
It is known that the compound [A] can be obtained by reacting a compound represented by formula [B]:
with 4(1H)-quinolinone compound represented by formula [C]:
and then reducing the reaction product with sodium borohydride (Patent literature 1). However, the corresponding optically active form per se or a method for preparing the same (optical resolution methods of racemic form, asymmetric synthesis methods and the like) has not been reported so far.
From the viewpoint of synthetic chemistry, upon preparing an optically active form of the compound [A], there is considered a method of using an optically active form of 1,2,3,4-tetrahydroquinoline compound represented by general formula [I]:
[wherein R1 represents a hydrogen atom or a protecting group for amino group.]as a synthetic intermediate, instead of using the compound [C]. However, the optically active compound [I] per se is a novel compound, and of course a method for preparing the same has not been reported so far. Under the circumstances, in order to establish a method for preparing an optically active form of the compound [A] comprising using the above-mentioned optically active compound [I], it is required to develop a method for preparing the optically active compound [I] with high optical purity and good yield.
[Patent literature 1] WO01/70700